CN110266411A - Low-complexity sequence detection method for dual-antenna telemetry system - Google Patents

Abstract

The invention provides a low-complexity Alamouti-SOQPSK-TG telemetry system sequence detection method. The technical scheme is that 32 XTCOM symbols are adopted to represent waveforms corresponding to branch paths in the state transition process. The method has the advantages that 32 XTCOM symbols are selected to represent possible waveforms of signals in every two code element periods, so that compared with a method adopting 8 waveform XTCOM, the method adopting 8 XTCOM symbols is more accurate and has higher detection precision; compared with a 2048 waveform XTCOM method which adopts 2048 XTCOM symbols to represent waveforms, the method has lower complexity.

Description

A low-complexity sequence detection method for dual-antenna telemetry systems

technical field

The invention relates to the technical field of wireless communication and telemetry and remote control, and provides a low-complexity Alamouti-SOQPSK-TG telemetry system sequence detection method.

Background technique

SOQPSK (Shaped Offset Quadrature Phase Shift Keying, Shaped Offset Quadrature Phase Shift Keying) has the advantages of continuous phase, constant envelope, high power efficiency and high spectrum efficiency. widely used. SOQPSK-TG (Shaped Offset Quadrature Phase ShiftKeying-Telemetry Group Version, telemetry version shaped offset quadrature phase shift keying) is a SOQPSK signal specially designed for telemetry systems. See reference 1 for the Alamouti-SOQPSK-TG telemetry system. The structure of the coding and modulation part of the sending end is shown in Figure 1. Suppose the binary sequence to be sent is b, and every 4 bits in the sequence b are divided into a code block (such as As shown in the dashed box, b _4k , b _4k+1 , b _4k+2 , and b _4k+3 are a code block), and two parallel sequences b ₀ and b ₁ are obtained through the Alamouti encoder. The four bits in sequences b ₀ and b ₁ corresponding to the code blocks in sequence b (as shown in the solid line box) are called Alamouti code blocks, as shown in Figure 1, is an Alamouti code block, is an Alamouti code block, and Corresponding to b _4k , b _4k+1 , b _4k+2 , b _4k+3 , respectively pass b ₀ and b ₁ through the SOQPSK-TG modulator to obtain two signals s ₀ and s ₁ and send them out with two antennas respectively. The structure of the receiving end is shown in Figure 2. An antenna is used to receive signals, and baseband processing, parameter estimation, timing and carrier synchronization, and sequence detection are performed on the received signals to obtain the transmission sequence b.

The sequence detection part of the receiving end of the Alamouti-SOQPSK-TG telemetry system usually corresponds to each possible combination of the 4 bits in the Alamouti code block as a possible state, and the signal waveforms corresponding to all possible branch paths during the state transition process are stored in advance , when performing sequence detection, first calculate the Euclidean distance between it and the received signal as the branch path metric increment, and finally use the Viterbi algorithm to complete the sequence detection. Reference 1 pointed out that the signal waveforms corresponding to all possible branch paths in the state transition process can be represented by XTCOM (Cross-correlated Trellis-coded Quadrature Modulation, cross-correlated trellis-coded quadrature modulation) symbols, and proposed the 8-waveform XTCOM method and The 2048 waveform XTCOM method and the 8 waveform XTCOM method can greatly reduce the complexity of detection, but the detection performance is poor; the 2048 waveform XTCOM method has better performance, but the complexity is extremely high, and it is basically impossible to realize.

Contents of the invention

The technical problem to be solved by the present invention is to provide a low-complexity Alamouti-SOQPSK-TG telemetry system sequence detection method. Compared with the 8-waveform XTCOM method, this method can reliably detect under the condition of lower signal-to-noise ratio; compared with the 2048-waveform XTCOM method, the computational complexity of this method is greatly reduced.

The technical solution of the present invention is: a low-complexity Alamouti-SOQPSK-TG telemetry system sequence detection method characterized in that 32 kinds of XTCOM symbols are used to represent the waveform corresponding to the branch path in the state transfer process.

The beneficial effects of the present invention are that the Alamouti-SOQPSK-TG telemetry system low-complexity sequence detection method provided by the present invention: select 32 kinds of XTCOM symbols to represent the possible waveforms of every two symbol period signals, compared to adopting 8 waveforms XTCOM Compared with the 2048 waveform XTCOM method using 2048 XTCOM symbols to represent waveforms, this method has lower complexity. Among them, 32 kinds of waveforms are used to represent 32 kinds of XTCOM symbols, especially through the specific implementation method proposed by the present invention, the perfect combination of low complexity and high detection accuracy is well realized.

Description of drawings

Figure 1 is a structural diagram of the sending end of the Alamouti-SOQPSK-TG telemetry system;

Figure 2 is a structural diagram of the receiving end of the Alamouti-SOQPSK-TG telemetry system;

Fig. 3 is the state transfer process figure when Alamouti code block;

Fig. 4 is the bit error performance figure that utilizes the present invention and existing method to be applied in Alamouti-SOQPSK-TG telemetry system to carry out emulation experiment;

Figure 5 is when , use the XTCOM symbol to represent the schematic diagram of the signal waveform corresponding to the k+1th Alamouti code block;

Figure 6 is when , the schematic diagram of the signal waveform corresponding to the k+1th Alamouti code block is represented by XTCOM symbols.

Detailed ways

The implementation process of the present invention will be described in detail below in conjunction with FIG. 3 , FIG. 4 and FIG. 5 . A low-complexity sequence detection method for Alamouti-SOQPSK-TG telemetry systems. Assuming that the sampling period of the baseband processing is T, each bit duration samples the received signal N times, and the estimated values of the channel response functions of the s ₀ and s ₁ signals are respectively The ratio of the estimated time delay difference between s ₀ and s ₁ signals to the sampling period T is (Assuming that the time delay of the s ₀ -way signal is greater than the time delay of the s ₁ -way signal, The time delay of s ₀ -way signal is less than the time delay of s ₁ -way signal, ), 4N discrete sequences r[4Nk],r[4Nk+1],r[4Nk+2],...,r[4Nk+4N-1] can be used to represent the baseband processing at the receiving end, parameter estimation, timing and A signal corresponding to the kth (k=1, 2, 3...) Alamouti code block sent by the transmitting end after carrier synchronization. During sequence detection, perform the following operations:

Step ①: Set the cumulative metric M ₁ of all possible states corresponding to the first Alamouti code block to be 0, then set k=1, and enter into step ②.

An Alamouti code block can be represented by 4-bit binary, that is, an Alamouti code block has 16 possible states in total. Each transmission of an Alamouti code block corresponds to a state transition. The state transition process when the k+1th Alamouti code block is transmitted is shown in Figure 3. The circle on the left represents the Alamouti code block at time k (that is, the corresponding codes of sequences b _k , b _k+1 , b _k+2 , and b _k+3 block), and the circle on the right indicates all possible states of the Alamouti code block at time k+1 (ie, the sequence b _k+4 , b _k+5 , b _k+6 , b _k+7 corresponds to the code block) , the number in the circle indicates a possible state (for example, "0000" corresponds to the state b _k = 0, b _k+1 = 0, b _k+2 = 0, b _k+3 = 0), and the line indicates the state transition Branch path, each circle on the left or right is connected with 16 lines, that is, each state on the left may undergo state transition along 16 branch paths, and each state in the circle on the right may be formed by any of the 16 states One is obtained through the import path.

Step ②: Calculate the metric increment of each branch path corresponding to the state transition that occurs when the k+1th Alamouti code block is transmitted, that is, when the state corresponding to the left circle is transferred to the state corresponding to the right circle as shown in Figure 3 The metric increment for each branch path.

The metric increment of the branch path when transmitting the k+1th Alamouti code block can be divided into two parts D _k+1,0 and D _k+1,2 . As shown in Figure 3, each branch path can be represented by the numbers in the two circles at the beginning and the end, such as the transition from state "0000" to state "0000" (that is, means b _k =0, b _k+1 =0, b _k+2 ＝0, b _k+3 ＝0, b _k+4 ＝0, b _k+5 ＝0, b _k+6 ＝0, b _k+7 ＝0) the corresponding branch path can be expressed as "00000000 ".

when _, the _metric increments _{D k + 1,0 and D k +} The calculation methods of ₁ and 1 are respectively:

when _, the _metric increments _{D k + 1,0 and D k +} The calculation methods of ₁ and 1 are respectively:

When k=0, each branch path has b _-4 =0, b _-3 =0, b _-2 =0, b _-1 =0; when k>0, the corresponding branch path "b _4k b _{4k+ 1} b _4k+2 b _4k+3 b _4k+4 b _4k+5 b _4k+6 b _4k+7 "The value of b _4k-4 , b _4k-3 , b _4k-2 , b _4k-1 can be determined by the state The sequence corresponding to the survival path of "b _4k b _4k+1 b _{4k+ 2} b _4k+3 " is obtained. For the method of obtaining the sequence corresponding to the survival path, refer to step ③. The above involves something like The general expression of calculation items in the form of ..., etc. is X ₃₂ (t; c ₁ ,···,c ₅ ), and its calculation method is:

t in the formula represents mT in the previous formula, etc., c ₁ ,...,c ₅ in the formula replace the different b _4k , b _4k+1 , b _4k+2 , b _4k+3 , b _4k+4 , b _4k+5 , b _4k+6 , b _4k+7 ; then the items on the right side of the first equal sign in the formula are represented by the general expression X(t; d ₁ ,d ₂ ,···,d ₁₁ ), and the calculation method is:

X(t; d ₁ ,d ₂ ,···,d ₁₁ )

＝cos(φ(t; d ₁ ,d ₂ ,···,d ₁₁ ))+jsin(φ(t;d ₁ ,d ₂ ,···,d ₁₁ ))

Where q(t) is the phase pulse function of SOQPSK-TG, q(t-iT _b ) means that q(t) delays iT _b in the time domain, and T _b is the duration of 1 bit, θ(0,1)=π, θ(1,0)=0,

Step ③: Calculate the cumulative metric SM _k+1 of the import path corresponding to the k+1th Alamouti code block, select and store the surviving paths of each state, and update the cumulative metric M _k+1 of each state; if the th If k+1 Alamouti code blocks are the last Alamouti code blocks, then step ④ is performed. Otherwise, set k=k+1, and proceed to step ②.

Among them, the calculation method of the cumulative metric SM _k+1 of the import path is:

SM _k+1 =M _k +D _k+1,0 +D _k+1,1

Among them, M _k represents the cumulative metric of the state corresponding to the circle on the left of the incoming path, and D _k+1,0 and D _k+1,0 represent the metric increments corresponding to the incoming path. After the calculation of the cumulative metrics of the 16 incoming paths in each state is completed, pick the incoming path with the smallest cumulative metrics as the surviving path of the state, and the corresponding sequence of the surviving path corresponds to the number in the circle on the left connected to the path . The cumulative metric of the surviving path is taken as the cumulative metric M _k+1 of the state.

Step ④: According to the Viterbi algorithm, detect the sending sequence.

After selecting the surviving paths of all states of the last Alamouti code block, select the state with the largest cumulative metric, find out the surviving path corresponding to this state as the final surviving path, and send the bit sequence corresponding to the state passed by this surviving path as The estimated value of the sequence.

Utilize the present invention and existing method to carry out emulation experiment to Alamouti-SOQPSK-TG telemetering system, the bit error performance of experiment is as shown in Figure 6, and dotted line represents the bit error performance of existing 8 waveform XTCOM method in the figure, and solid line represents Bit error performance of the present invention, the abscissa represents E _b /N ₀ (the ratio of signal energy per bit to the noise power spectral density), and the ordinate represents the bit error rate, and the dotted line with a circle represents Bit error performance of XTCOM method with 8 waveforms at 0:00, indicated by a dotted triangle line The bit error performance of the 8-waveform XTCOM method when -5 is represented by the solid line with circles The bit error performance of the XTCOM method with 0:32 waveform, indicated by the solid triangle line The bit error performance of the XTCOM method with 32 waveforms at -5. The experimental parameters are: the number of sampling points for each symbol is N=16, the phase difference θ=0.1π of the channel response, the ratio of the time delay difference of the two signals to the sampling period 0 and -5 respectively, the power of the two transmitting antennas is equal. It can be seen from the figure:

① When the bit error rate is 10 ^-5 , When it is 0, the 32-waveform XTCOM method shown in the present invention can save about 1.2dB of E _b /N ₀ compared with the 8-waveform XTCOM method; when the bit error rate is 10 ^-5 , When it is -5, the 32-waveform XTCOM method shown in the present invention can save about 1.4dB of E _b /N ₀ compared with the 8-waveform XTCOM method. It shows that this method can complete the detection under the condition of lower signal-to-noise ratio than the existing method.

② When the bit error rate is 10 ^-5 , When it is -5, the E _b /N ₀ required by the present invention is only 0.3dB more than 0. It shows that the time delay difference between the two signals has little effect on the detection performance of this method.

Figures 5 and 6 illustrate the basics of how to represent local signals with 32 XTCOM symbols. Figure 5 corresponds to case, Figure 6 corresponds to Case.

As shown in Figure 5, the bit sequence corresponding to the k+1th Alamouti code block s ₀ is According to the method shown in Document 2, the bit sequence is transmitted Represented by two XTCOM symbols, the first XTCOM symbol corresponds to b _4k+4 , b _4k+5 , and the second XTCOM symbol corresponds to Document 2 only gives the possibility of representing the waveform of the first XTCOM symbol or the second XTCOM symbol with at least 3 bits and a maximum of 11 bits. 3 bits represent 8 kinds of XTCOM symbols, and 11 bits correspond to 2048 An XTCOM symbol, but because the scene corresponding to Document 2 is a single antenna with only one signal, it does not give any enlightenment on how to represent the waveform of the two signals. According to the inventor's earnest exploration and research, the present invention proposes to use 32 kinds of XTCOM symbols to represent the possible waveform correspondence of every two symbol period signals, that is, to use 5 bits to represent the corresponding 32 kinds of XTCOM symbols. First of all, 5 bits are chosen instead of other numbers because it is found through research that an even number of bits cannot complete the effective representation of the signal, and secondly, choosing 5 bits can achieve an effective compromise between complexity and accuracy. Under the situation of adopting 5bit, how to carry out the effective expression of waveform, then adopt the method described above of the present invention, discuss again emphatically below:

The bit sequence corresponding to the k+1th Alamouti code block s ₀ way is transmit bit sequence Represented by two XTCOM symbols, the first XTCOM symbol corresponds to b _4k+4 , b _4k+5 , and the second XTCOM symbol corresponds to The waveform of the first XTCOM symbol can be determined by the previous bit sequence To determine, the waveform of the second XTCOM symbol can be determined by the previous bit sequence To determine, the expressions of the two XTCOM symbols can be expressed by the aforementioned formula one X ₃₂ (t; c ₁ ,···,c ₅ ). As shown in Figure 5, due to the time delay between the _s0 signal and the _s1 signal, the time occupied by each XTCOM symbol of the _s0 signal corresponds to the two _XTCOM symbols of the _s1 signal; The time occupied by the k+1th Alamouti code block corresponds to three XTCOM symbols of the _s1 -channel signal. Therefore, as shown in Figure 5, the first XTCOM symbol of the s ₁ -way signal can be represented by the bit sequence To determine, the second XTCOM symbol of the s ₁ -way signal can be determined by the bit sequence To determine, the third XTCOM symbol of the s ₁ channel signal can be determined by the bit sequence b _4k+2 , b _4k+3 , b _4k , b _4k+1 , b _4k+6 . Therefore, each XTCOM symbol corresponds to ²⁵ kinds of waveforms. when , similarly, as shown in Figure 6.

Reference 1: Rice M, Nelson T, Palmer J, et al. Space-Time Coding for Aeronautical Telemetry: Part II—Decoder and System Performance [J]. IEEE Transactions on Aerospace & Electronic Systems, 2017, 53(4): 1732-1754. Reference 2: REDUCED COMPLEXITY TRELLIS DETECTION OF SOQPSK-TG. International Telemetering Conference Proceedings.

Claims (2)

1. a kind of Alamouti-SOQPSK-TG telemetry system sequence detecting method of low complex degree, SOQPSK-TG refer to telemetering Version shaped offset quadrature phase shift keying, which is characterized in that indicate branch path in state migration procedure using 32 XTCOM symbols The corresponding waveform of diameter.

2. the Alamouti-SOQPSK-TG telemetry system sequence detecting method of low complex degree according to claim 1, It is characterized in that, the corresponding waveform of individual path, specific implementation side in state migration procedure is indicated using 32 XTCOM symbols Formula are as follows:

When transmitting+1 Alamouti code block of kth, the measurement increment of individual path is divided into D_k+1,0And D_k+1,2Two parts；

WhenWhen, the measurement increment D of individual path_k+1,0And D_k+1,1Calculation method be respectively as follows:

WhenWhen, the measurement increment D of individual path_k+1,0And D_k+1,1Calculation method be respectively as follows:

The generic representation of the above-mentioned computational item being related to is X₃₂(t；c₁,…,c₅), calculation method are as follows:

The items of one right side of the equal sign of formula use expression X (t；d₁,d₂,…,d₁₁) indicate, calculation method are as follows:

X(t；d₁,d₂,…,d₁₁)

=cos (φ (t；d₁,d₂,…,d₁₁))+jsin(φ(t；d₁,d₂,…,d₁₁))

Wherein q (t-iT_b) indicate that phase impulse function q (t) postpones iT in the time domain_b, T_bFor 1 bit duration,θ (0,1)=π, θ (1,0)=0,